Parallel Jets Research Articles

Three-dimensional modeling of the gas field distribution of a high-pressure gas jet used in laser fusion cutting

A three-dimensional mathematical model for investigating theoretically the gas flow field distribution of the free exit gas jet from both subsonic and supersonic nozzles under the regime of high-pressure gas-assisted laser fusion cutting is presented in this article. The influence of the flow nonuniformity in the subsonic nozzle exit upon the field distribution in the free gas jet is considered in this model. The calculated results are in good agreement with those observed by shadowgraphy. The relationships between the inlet stagnation pressure and the flow field distribution, incident shock, and normal shock of a gas jet in free space are established. The processing characteristics of the free space gas jet in the high-pressure gas-assisted laser cutting process for both subsonic and supersonic nozzles are analyzed in detail. Compared with that from the subsonic nozzle, such as the commonly used conical or conical–cylindrical nozzle, the gas jet from the supersonic nozzle (Laval nozzle) possesses good features such as uniform distribution, maximum even momentum thrust, and a parallel jet boundary under the condition of the designed “working pressure.”

Experimental and Numerical Investigation of Two-Dimensional Parallel Jets

The flowfield of dual, parallel planar turbulent jets is investigated experimentally using an x-type hot-wire probe and numerically by solving the Reynolds-averaged Navier-Stokes equations. The performance of both differential Reynolds stress (RSM) and standard k-ε turbulence models is evaluated. Results show that the numerical models predict the merge and combined point characteristics to good accuracy. However, both turbulence models show a narrower width of the jet envelope than measured by experiment. The predicted profiles of the mean velocity along the symmetry plane agree well with the experimental results.

1111 近接二平面噴流の流動特性に関する研究(G.S.9 流体工学II)

1111 近接二平面噴流の流動特性に関する研究(G.S.9 流体工学II)

Interaction of Multiple Gas Jets Horizontally Injected into a Vertical Water Stream

A gas jet injected horizontally into a descending vertical water flow has two stable states corresponding to the presence or absence of a gas pocket on the injection wall. Injecting multiple parallel jets gives rise to complex interactions dominated by two phenomena: the presence or absence of a gas pocket and the periodic movements of the jets. The very low frequency of these movements (approx. 1 Hz) is essentially correlated with crossflow velocity and jet spacing. Different types of interaction were observed over a wide range of experimental conditions. In particular, a zone of interdependence was evidenced where interaction between jets leads to the coexistence of jets with and without a gas pocket. The influence of different experimental parameters was defined. A better understanding of the mechanism of jet interaction is obtained, especially the conditions of movement of vortices and the significance of the water flow confined between the jets which modifies their mean dimensions (20 to 40% increase in length and height, decrease of width without coalescence).

LDV Measurement of Confined Parallel Jet Mixing

Laser Doppler Velocimetry (LDV) measurements were taken in a confinement, bounded by two parallel walls, into which issues a row of parallel jets. Two-component measurements were taken of two mean velocity components and three Reynolds stress components. As observed in isolated three-dimensional wall bounded jets, the transverse diffusion of the jets is quite large. The data indicate that this rapid mixing process is due to strong secondary flows, transport of large inlet intensities, and Reynolds stress anisotropy effects.

201 平行噴流に発生する渦列について(流体工学-噴流・希薄流体1)

201 平行噴流に発生する渦列について(流体工学-噴流・希薄流体1)

DSMC Simulation of Parallel, Oblique and Normal Free Jet Impingements on a Flat Plate.

In the present paper, jet impingements of gas expanded through an orifice into a vacuum were numerically simulated by using the direct simulation Monte Carlo (DSMC) method. Three types of jet impingement, parallel, oblique and normal, were treated. The parallel and oblique impingements were considered as a three-dimensional problem, whereas normal impingement was treated as an axisymmetric problem. The numerical simulations were carried out using the variable soft sphere (VSS) model for nitrogen. For the energy exchange between translational and rotational modes, the Borgnakke-Larsen model was employed together with the temperature-dependent energy exchange probability of Boyd. Simulated results were compared with Legge’s experiments and a simple impingement model in the range of the reservoir pressures from 0.1×104 to 1.6×104 Pa. The present results agreed well with Legge’s experimental data of pressure and shear stress distributions on a flat plate.

1925 二次元平行噴流の特性について

This paper describes characteristic features of flow patterns that were experimentally analyzed in the transision region of the two dimensional parallel jet with parabolic velocity distribution. The asymmetrical vortex street or symmetrical vortex street was observed in the jet of water shot out from the slot into two dimensional flow field. There were the asymmetrical voltex street at low Reynolds number, and symmetrical voltex street at hight Reynolds number determind by the width 2b of slot and the jet velocity U at slot. These results fitted the linear approximation mathmatical model by Euler's kinetic equation and continuity equation.

An investigation on parallel, divergent and convergent acetylene dual jet diffusion flames

Results are presented and discussed of an experimental investigation on acetylene turbulent dual jet diffusion flames. The study includes parameters of flames in parallel, divergent and convergent configurations. Tests with two parallel jets with addition of helium in the fuel stream were also performed and analysed. The variation of overall flame length and of other flame physical characteristics, such as width, volume and conditions for lifting, are presented as functions of burner tip Reynolds number, jet distance from each other and inclination angle. The effects of diluent concentration in the fuel gas stream are presented for single and two parallel jets.

Subaru Sees an Unruly Pair

A pair of embryonic stars, swaddled in gas and dust, emit parallel jets in this image from Japan9s new 8.3-meter Subaru Telescope on Mauna Kea in Hawaii. The Hubble Space Telescope discovered the jets, but Subaru is the first Earth-based telescope to see them.

Echocardiographic characteristics of transprosthetic blood peak velocity in the Sorin Bicarbon bileaflet prosthetic heart valve

The Bicarbon prosthetic heart valve with two curved leaflets is designed so that the blood flows through the three orifices are parallel jets of equal size. This study was conducted to confirm that the Bicarbon valve functions clinically as designed. Forty-three patients underwent valve replacement with the Bicarbon valve. Forty-eight Bicarbon valves were implanted: 25 valves in the mitral position and 23 in the aortic position. Peak blood flow velocity through the three prosthetic orifices was measured postoperatively by Doppler echocardiography. The three flow jets through the prosthesis were parallel. The velocity through the lateral orifice was 2.33±0.38 m/min, and the velocity through the central orifice was 2.14±0.43 m/min at the aortic position (P>0.05). The velocity through the lateral orifice was 1.72±0.06 m/min at the mitral position, and that through the central orifice was 1.73±0.06 m/min (P>0.05). Serum lactic acid dehydrogenase values were also lower than those of patients or whom another bileaflet prosthesis had been implanted. The results confirm that the Bicarbon prosthetic heart valve performs clinically as designed, producing three parallel blood flow jets with equal flow velocity.

Concentration field of multiple circular turbulent jets

The Reichardt hypothesis on the lateral transport of momentum has been used previously to predict the velocity field of multiple turbulent jets. In this paper, based on an extension of the Reichardt hypothesis to the lateral transport of pollutant, a method has been developed to predict the concentration field of multiple circular turbulent jets discharged into a large stagnant ambient. Experimental observations from one experiment with three parallel jets support the theoretical predictions.

Three Dimensional DSMC Calculation for Plume-Plume Interaction of Parallel Supersonic Jets.

Three dimensional interacting flowfield of two parallel axisymmetric jets is calculated by the DSMC method. Under limited computer resource it is not easy to simulate the three dimensional flowfield using the method, because every volume of cell is very small and the number of molecules within the cell becomes also very small. In the present calculation the upstream flowfield of each orifice is assumed to be axisymmetric and only the downstream of the orifice is managed to be three dimensional although the downstream flowfield is restricted within one fourth of the full flowfield. The secondary jet-cell that is formed with two barrel shocks of the two primary jets can be seen clearly in the middle between the jets. The fundamental flow structure calculated by the DSMC method is compared with the experimental result of flow visualization by the laser induced fluorescence technique.

Two parallel plane jets: Comparison of the performance of three turbulence models

There have been many investigations in the literature to examine the performance of different turbulence models in predicting flow over backward-facing steps where the flow is bounded by solid boundaries. However, the evaluation of different turbulence models in predicting free shear layers with no solid boundaries, such as two parallel plane jets, is limited. In this paper, the velocity field of two parallel plane jets with a small nozzle separation ratio of s/ w = 4:25 determined by laser Doppler anemometry (LDA) is first presented. These experimental results are used to examine the performance of three turbulence models (i.e. k - ɛ, RNG k - ɛ and Reynolds stress) in predicting this flow field. The effects of computational domain size, grid resolution and different discretization schemes on the predictions are discussed. The existence of a recirculation flow region, a merging region and a combined region in the two parallel plane jet configuration has been predicted qualitatively by all three turbulence models. On the other hand, quantitative agreement between predictions and measurements varied by as much as 18 per cent for the merging length while the jet spread in the outer shear layer has been substantially under- predicted by all three models.

Theory and modelling of the interaction of two parallel supersonic plasma jets

The objective of the present work is to predict the profile of the shock front formed by the interaction of two parallel diverging supersonic plasma jets. The form of the front is determined by the divergence of the plasma jets and by the distance between their sources, but the maximum angle of the front inclination at the head point of the shock wave is determined by the plasma properties only. The streamlines of the two plasma jets are diverging before the front and are parallel behind it. The diffusion of the ions flying from two different sources was calculated numerically up to a distance of 10 times the source separation in the region bounded by two symmetric shock fronts. For an ion temperature of K, a jet velocity of , and initial densities of and (corresponding to a Mach number of 10 and Knudsen numbers of 0.04 and 0.4 respectively) the partial and total density distribution in the diffusion zone was found. The ion distribution is not homogeneous in all of investigated regions. The most homogeneous distribution was obtained with an initial density of . The shock model predictions were compared with a free expansion model, and the densities are radically different.

Turbulence-Induced Tube Vibration by Parallel Air-Water Two-Plase Jet Flow.

In many shell and tube heat exchangers such as steam generators, baffle plates are located at appropriate intervals to support the heat transfer tubes. In the heat exchangers, the secondary coolant streams through the channels such as the flow hole nozzles of the baffle plates in the form of jets, and flows in parallel with the tube bundle. This turbulence induces vibrations which could cause fretting wear and fatigue of the tubes. In this paper, basic characteristics of tube vibration were experimentally investigated in air water two phase flow to evaluate the jet effect on the relationships between hydrodynamic mass, damping ratio, and excitation force on a vibrating tube and void fractions.

Distribution of metal onto the belt of a horizontal strip caster

This paper presents a new method for metal distribution onto the belt of a horizontal single belt strip caster. Water and liquid tin have been used to study the flow conditions in the feeding zone on the conveyor belt. Tests of a method presented in literature for metal distribution have been conducted and a new method that uses multiple parallel jets in order to obtain stable feeding conditions have been tested. This method gives a controlled way of maintaining a continuous liquid film and it also has a stable meniscus. The freezing problem with a triple point will also be eliminated by use of this method.

Instability properties of interacting jets

Two parallel circular jets, in inviscid incompressible flow, with uniform axial velocity of the same magnitude and direction are placed near to one another, resulting in a strongly coupled field. A given (small) wavenumber in the axial direction is taken and a dispersion relation is found relating the frequency and wavenumber for a given disturbance mode, along with the velocity potentials within and exterior to the jets. The problem is tackled analytically using bipolar coordinates and asymptotic forms for the dispersion relation are found in the small-separation and large-separation limits. Results are then compared with the corresponding two-dimensional problem for plane jets. It is concluded that close-proximity interactions greatly destabilize the varicose mode of the coupled jet, and greatly stabilize the sinuous mode.

Comparison of flow characteristics in the near field of two parallel plane jets and an offset plane jet

Two parallel plane air jets and offset air jets have several common features such as the existence of a subatmospheric pressure region and the formation of a flow recirculation zone adjacent to the nozzle plate. In particular, the symmetry plane that exists between two parallel plane jets may appear to affect the flow field in much the same way as a solid wall does in a reattaching offset jet. It is obvious, however, that there are significant differences far downstream from the nozzles because the two parallel plane jets will combine to form a single free jet while the offset jet will develop into a wall jet. Differences in the near field between these two jet configurations with a separation ratio of 2.125 are examined here under identical initial flow exit conditions through laser Doppler anemometer measurements of the mean velocity components, turbulence intensities, and Reynolds shear stress. The results indicate that the wall exerts significant retarding and turbulence suppression effects on the offset jet in the flow development region. Through the use of comparisons, the interaction of two inner shear layers on both sides of the symmetry plane in two parallel plane jets results in a much more turbulent near field than that of the offset jet.

Chemical oxygen — iodine laser with mixing of supersonic jets

The results are reported of the first investigation of a chemical oxygen — iodine laser with supersonic mixing of parallel jets of oxygen and of a mixture of nitrogen with iodine. It was found that, in principle, such a laser system is feasible. The maximum output power was 160 and 130 W with the chemical efficiency 13% and 14.3%, respectively. An analysis of the results of a numerical calculation indicated that the investigated method of formation of the active medium is promising.